Tobias is a Labrador retriever with one job: sniffing out invasive Argentine ants wherever they hide. He’s really good at it, and with his help, a fragile island ecosystem may be spared a repeat inundation with the pests.

Santa Cruz Island is 25 miles off the coast of Southern California, part of Channel Islands National Park. The island’s rich, rugged environment — which includes more than 1,000 kinds of plants and animals, including the bald eagle and the island fox — is threatened by Argentine ants, one of the world’s most successful and wily invasive species.

The ants are one in a long line of threats that The Nature Conservancy has worked to overcome since it bought most of the island in 1978. In one section, the ants chased away flower-pollinating bees, native ants, spiders and other insects crucial to local ecology.

They are nearly impossible to get rid of; it had never been done with an infestation as large as Santa Cruz’s. But Christina Boser, an ecologist who leads the conservancy’s ant eradication project, devised an aerial assault, dropping tiny sugar water beads spiked with diluted poison from helicopters.

An Argentine ant. They have become major pests on six continents.Credit Sarah Gregg

The campaign, largely in 2015 and 2016, appears to have killed off the ants. Still, if even one colony has survived, this elaborate effort might have been wasted.

That’s where Tobias comes in. Once he pinpoints the faint pheromone scent left by this particular species of ant — and no other — he will sit down and look at his handler with the excited expectation of a child on Christmas morning. Tobias’s reward is his “wubba,” a soft blue ball.

“We have developed a really special bond,” said Kyren Zimmerman, a handler with the nonprofit Working Dogs for Conservation, headquartered in Bozeman, Mont.

Dogs are renowned for their scenting skills, whether they’re detecting narcotics, bedbugs, bombs or tumors. Increasingly, since the 1990s, scientists have trained them to aid in conservation.